I would suspect that part of the reasoning for replacement is that the manufacturer has no control over how the machine is operated. Are shifts being done without benefit of clutch disengagement, or is the operator riding like an old fart?
I can see the shock loads when bang shifting being pretty tough on clutch bolts(as well as splines and transmission bits), as opposed to smoothly disengaging and re-engaging the clutch when shifting. Shifting gently makes it possible for me to save a bunch of cash when I service my clutch.
